APP and Alzheimer disease: It is necessary to understand that many solid studies support connections between AD and aberrant protein glycosylation, considering the fact that glycoproteins including tau, Aβ-precursor protein (APP), and β-site APP-cleaving enzyme-1 (BACE-1) are involved in AD pathogenesis and have been found to show altered glycosylation patterns (Halim et al., 2011; Schedin-Weiss et al., 2014, 2019; Kizuka et al., 2015).